POJ 3352

题目大意：给出一副图，求这幅图上可能的生成树中，树的最大边与最小边的差的最小值为多少；

解：枚举最小边，kruskal，然后求出最大的一条边，询问，与答案比较。因为kruskal的最优，所以最小边一定的时候得到的生成树的最大边一定是最小的，注意无解输出1。还有记得并茶几的初始化。

View Code 
  1 //poj 3352
  2 const
  3         maxn=1111;
  4         maxm=1111;
  5 type
  6         data=record
  7           next, dest, op: longint;
  8         end;
  9 var
 10         edge: array[1..maxn*2]of data;
 11         deg, pre, dist, low, dfn, vect: array[1..maxn]of longint;
 12         visit: array[1..maxn]of boolean;
 13         time, stot, ans, tot, n, m: longint;
 14 procedure add(x, y: longint);
 15 begin
 16   inc(tot);
 17   with edge[tot] do begin
 18     dest := y;
 19     next := vect[x];
 20     vect[x] := tot;
 21     op := tot + 1;
 22   end;
 23   inc(tot);
 24   with edge[tot] do begin
 25     dest := x;
 26     next := vect[y];
 27     vect[y] := tot;
 28     op := tot - 1;
 29   end;
 30 end;
 31 
 32 procedure init;
 33 var
 34         i, j, x, y: longint;
 35 begin
 36   ans := 0; tot := 0;
 37   fillchar(vect, sizeof(vect), 0);
 38   readln(n, m);
 39   for i := 1 to m do begin
 40     readln(x, y);
 41     add(x, y);
 42   end;
 43 end;
 44 
 45 procedure tarjan(x: longint);
 46 var
 47         i: longint;
 48 begin
 49   inc(time);
 50   low[x] := time; dfn[x] := time;
 51   visit[x] := true;
 52   i := vect[x];
 53   while i<>0 do
 54     with edge[i] do begin
 55      if pre[x]<>dest then
 56       if dfn[dest]=0 then begin
 57         pre[dest] := x;
 58         tarjan(dest);
 59         pre[dest] := 0;
 60         if low[dest]<low[x] then low[x] := low[dest];
 61       end
 62         else if visit[dest] then begin
 63           if dfn[dest]<low[x] then low[x] := dfn[dest];
 64         end;
 65       i := next;
 66     end;
 67   visit[x] := false;
 68 end;
 69 
 70 procedure main;
 71 var
 72         i, u: longint;
 73 begin
 74   fillchar(dfn, sizeof(dfn), 0);
 75   fillchar(visit, sizeof(visit), 0);
 76   time := 0; stot := 0;
 77   for i := 1 to n do
 78     if dfn[i]=0 then tarjan(i);
 79   fillchar(deg, sizeof(deg), 0);
 80   for u := 1 to n do begin
 81     i := vect[u];
 82     while i<>0 do
 83       with edge[i] do begin
 84         if low[u]<>low[dest] then begin
 85           inc(deg[low[u]]);
 86           inc(deg[low[dest]]);
 87         end;
 88         i := next;
 89       end;
 90   end;
 91   for i := 1 to maxn do
 92     if deg[i] >> 1 = 1 then inc(ans);
 93   if ans=1 then ans := 0;
 94   ans := (ans+1)>>1;
 95 end;
 96 
 97 procedure print;
 98 begin
 99   writeln(ans);
100 end;
101 
102 begin
103   assign(input,'1.txt'); reset(input);
104   init;
105   main;
106   print;
107 end.
posted @ 2012-04-10 12:33  F.D.His.D  阅读(167)  评论(0)  编辑  收藏  举报